Honeycomb structure

ABSTRACT

The honeycomb structure of the present invention has a construction wherein a plurality of cells  5  each functioning as a passage of a fluid, surrounded by porous partition walls  6  are arranged so as to be parallel to each other in the central axis direction of the honeycomb structure, and has such a constitution that a plurality of honeycomb segments  2  are bonded integrally by a bonding material  9  containing a ceramic as a main component and a particulate filler. In the honeycomb structure, generation of drawbacks such as peeling of bonded area, cracking and the like is suppressed reliably, and the honeycomb structure is superior in durability.

TECHNICAL FIELD

The present invention relates to a honeycomb structure wherein aplurality of honeycomb segments are bonded integrally by a bondingmaterial. More particularly, the present invention relates to ahoneycomb structure which is useful particularly as a filter forcapturing, for example, the particulate present in an exhaust gas, inwhich the generation of drawbacks (e.g. peeling of bonded area andcracking) after bonding with bonding material, or the generation ofdrawbacks (e.g. small holes and cracking) after coating with coatingmaterial is suppressed reliably, and which is superior in durability.

BACKGROUND ART

As a filter for exhaust gas, a diesel particulate filter (DPF), forexample, is incorporated in, for example, the exhaust gas system ofdiesel engine in order to capture and remove the particulate containedin the exhaust gas emitted from the diesel engine or the like. Filtersfor exhaust gas such as the above DPF and the like are constituted by ahoneycomb structure wherein a plurality of honeycomb segments are bondedintegrally by a bonding material.

Such a honeycomb structure has a construction wherein a plurality ofcells each functioning as a passage of a fluid, surrounded by porouspartition walls made of a silicon carbide, etc. are arranged so as to beparallel to each other in the central axis direction of the honeycombstructure. In producing the honeycomb structure, a plurality ofhoneycomb segments having such a shape that each segment is part of thehoneycomb structure and, when bonded to each other in a direction normalto the central axis of the honeycomb structure, forms the honeycombstructure, are bonded integrally by a bonding material to obtain abonded body having an intended sectional shape (e.g. a circle) when cutby a plane normal to the central axis direction of the bonded body;then, the outer surface of the bonded body is coated with a coatingmaterial. At each end face of the honeycomb structure, the ends of cellsadjacent to each other are plugged alternately. That is, one cell isopen at one end face and plugged at other end face, and any other celladjacent thereto is plugged at the same one end face and open at thesame other end face.

By producing the honeycomb structure in the above constitution, anexhaust gas can be taken into the honeycomb structure from each one endof given cells, i.e. gas-incoming cells, be moved into cells adjacent tothe gas-incoming cells, i.e. gas-leaving cells, via porous partitionwalls, and be discharged out of the honeycomb structure from thegas-leaving cells; during the movement of the exhaust gas through thepartition walls, the particulate present in the exhaust gas can becaptured by the partition walls and thereby the exhaust gas can bepurified.

The bonding material for bonding a plurality of honeycomb segmentsintegrally and the coating material for coating the outer surface of theresulting bonded body, both used in production of the honeycombstructure are required to have good coatability. In particular, thebonding material is required to also show good spreadability inpress-bonding of honeycomb segments. In order for the bonding materialand the coating material to have such properties, it is effective tolower their viscosities when they re coated. However, a low-viscositybonding material and a low-viscosity coating material need to contain alarge amount of a solvent, making large the shrinkage caused by solventremoval during drying. As a result, after bonding with the bondingmaterial, drawbacks such as peeling of bonded area, cracking and thelike have tended to generate; and, after coating with the coatingmaterial, drawbacks such as small holes, cracking, fretting and the likehave tended to generate.

As a countermeasure for the above problem, there was disclosed (see apatent literature 1) a ceramic structure wherein an organic binder isadded to a bonding material in order to suppress the migration takingplace during drying and curing, consequently suppress theabove-mentioned drawbacks, and provide a honeycomb structure of improveddurability.

In the patent literature 1, as preferred examples of the organic binder,there are mentioned polyvinyl alcohol, methyl cellulose, ethyl celluloseand carboxymethyl cellulose. In the literature, it is disclosed that ofthese organic binders, carboxymethyl cellulose is preferred because itcan ensure fluidity of bonding material during bonding.

Patent literature 1: JP-B-3121497

DISCLOSURE OF THE INVENTION

The bonding material used in the ceramic structure disclosed in thepatent literature 1 ensures fluidity during bonding. However, thebonding material gives rise, during its kneading, to a change of statecaused by the addition of an organic binder, that is, viscosity increaseat the start of kneading and viscosity decrease during continuedkneading; thus, the bonding material has unstable properties, and it isdifficult to obtain good coatability and good spreadability, and, infact, it has been difficult to reliably control generation of theabove-mentioned drawbacks.

The present invention has been made in view of the above-mentionedproblems and aims at providing a honeycomb structure which is usefulparticularly as a filter for capturing, for example, particulatespresent in an exhaust gas, in which the generation of drawbacks (e.g.peeling of bonded area and cracking) after bonding with bondingmaterial, or the generation of drawbacks (e.g. small holes and cracking)after coating with coating material is suppressed reliably, and which issuperior in durability.

The present invention provides the following honeycomb structure inorder to achieve the above aim.

-   [1] A honeycomb structure comprising:    -   porous partition walls, and    -   a plurality of cells each functioning as a passage of a fluid,        surrounded by the porous partition walls and arranged so as to        be parallel to each other in the central axis direction of the        honeycomb structure,    -   characterized in that a plurality of honeycomb segments having        such a shape that each segment is part of the honeycomb        structure and, when bonded to each other in a direction normal        to the central axis of the honeycomb structure, forms the        honeycomb structure, are bonded integrally by a bonding material        containing a ceramic as a main component and a particulate        filler.

By employing such a constitution, it is possible to reliably suppressthe generation of drawbacks such as peeling of bonded areas, crackingand the like after bonding with a bonding material and achieveimprovement in durability. That is, by using a particulate filler, thefiller rolls easily in the bonding material (the rollability of filleris improved) and the bonding material can show good spreadability duringcoating of the bonding material or during press-bonding. As a result,improved coatability and improved spreadability are obtainable, it isnot necessary to use a large amount of a solvent for viscosity reductionof bonding material, dehydration and shrinkage during drying can besuppressed, and generation of the above-mentioned drawbacks duringdrying can be suppressed. Further, since the viscosity change duringkneading is small, the bonding material is stable, the control forimprovement in coatability and spreadability of bonding material iseasy, and generation of the above-mentioned drawbacks during drying canbe suppressed reliably.

In a honeycomb structure according to an exemplary embodiment, theparticulate filler contained in the bonding material has an averagediameter of 10 to 300 μm.

By employing such a constitution, the filler can secure rollability andthe bonding material can have good dryability.

In a honeycomb structure according to an exemplary embodiment, theparticulate filler contained in the bonding material has a hollowstructure.

By employing such a constitution, the bonding material can have a lowerYoung' modulus, the honeycomb structure can have higher thermal shockresistance, and the generation of cracking during use can be suppressedmore reliably.

In a honeycomb structure according to an exemplary embodiment, thebonding material contains the particulate filler in an amount of 20 to70% by volume.

By employing such a constitution, the bonding material can securecoatability and spreadability and can have a strength, and improveddurability is obtainable.

In a honeycomb structure according to an exemplary embodiment, thebonding material further contains at least one member selected from thegroup consisting of inorganic particles, an oxide fiber and a colloidaloxide.

By employing such a constitution, the bonding material can have improvedcoatability and improved spreadability.

-   [6] A honeycomb structure comprising:    -   porous partition walls, and    -   a plurality of cells each functioning as a passage of a fluid,        surrounded by the porous partition walls and arranged so as to        be parallel to each other in the central axis direction of the        honeycomb structure,    -   characterized in that a plurality of honeycomb segments having        such a shape that each segment is part of the honeycomb        structure and, when bonded to each other in a direction normal        to the central axis of the honeycomb structure, forms the        honeycomb structure, are bonded integrally by a bonding material        and the resulting bonded body is coated, at the outer surface,        with a coating material containing a ceramic as a main component        and a particulate filler.

By employing such a constitution, it is possible to reliably suppressthe generation of drawbacks such small holes, cracking and the likeafter coating with a coating material. That is, by using a particulatefiller, the filler rolls easily in the coating material (the rollabilityof filler is improved) and the bonding material can show goodspreadability during coating of the coating material or duringpress-bonding. As a result, improved coatability and improvedspreadability are obtainable, it is not necessary to use a large amountof a solvent for viscosity reduction of bonding material, dehydrationand shrinkage during drying can be suppressed, and generation of theabove-mentioned drawbacks during drying can be suppressed. Further,since the viscosity change during kneading is small, the coatingmaterial is stable, the control for improvement in coatability andspreadability of coating material is easy, and generation of theabove-mentioned drawbacks during drying can be suppressed reliably.

In a honeycomb structure according to an exemplary embodiment, theparticulate filler contained in the coating material has an averagediameter of 10 to 300 μm.

By employing such a constitution, the filler can secure rollability andthe coating material can have good dryability.

In a honeycomb structure according to an exemplary embodiment, theparticulate filler contained in the coating material has a hollowstructure.

By employing such a constitution, the coating material can have a lowerYoung' modulus, the honeycomb structure can have higher thermal shockresistance, and the generation of cracking during use can be suppressedmore reliably.

In a honeycomb structure according to an exemplary embodiment, thecoating material contains the particulate filler in an amount of 20 to70% by volume.

By employing such a constitution, the coating material can securecoatability and spreadability and can have a strength, and improveddurability is obtainable.

In a honeycomb structure according to an exemplary embodiment, thecoating material further contains at least one member selected from thegroup consisting of inorganic articles, an oxide fiber and a colloidaloxide.

By employing such a constitution, the coating material can have improvedcoatability and improved spreadability.

As described above, according to the present invention, there isprovided a honeycomb structure which is useful particularly as a filterfor capturing, for example, particulates present in an exhaust gas, inwhich the generation of drawbacks (e.g. peeling of bonded area andcracking) after bonding with bonding material, or the generation ofdrawbacks (e.g. small holes and cracking) after coating with coatingmaterial is suppressed reliably, and which is superior in durability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically showing one embodiment of thehoneycomb structure of the preset invention, having a circular sectionalshape when cut in a plane normal to the central axis.

FIG. 2 is a front view when part of other embodiment of the honeycombstructure of the present invention, having a square sectional shape whencut in a plane normal to the central axis, has been seen from the endface.

FIG. 3 is a perspective view schematically showing a honeycomb segmentused in other embodiment of the honeycomb structure of the presentinvention.

FIG. 4 is a sectional view taken at the A-A line of FIG. 3.

FIG. 5 is a graph showing the change of viscosity of bonding materialwith time, caused by kneading.

EXPLANATION OF SYMBOLS

1 is a honeycomb structure; 2 is a honeycomb segment; 4 is a coatingmaterial; 5 is a cell; 6 is a partition wall; 7 is a plugging material;and 9 is a bonding material.

BEST MODE FOR CARRYING OUT THE INVENTION

As shown in FIGS. 1 and 2, the honeycomb structure 1 according to theembodiment of the present invention has a construction wherein aplurality of cells 5 each functioning as a passage of a fluid,surrounded by porous partition walls 6 are arranged so as to be parallelto each other in the central axis direction of the honeycomb structure1, and has such a constitution that a plurality of honeycomb segments 2having such a shape that each segment is part of the honeycomb structure1 and, when bonded to each other in a direction normal to the centralaxis of the honeycomb structure 1, forms the honeycomb structure 1, arebonded integrally by a bonding material 9 containing a ceramic as a maincomponent and a particulate filler. By the bonding of the honeycombsegments 2 with the bonding material 9, a bonded body is formed; it issubjected to grinding so that the ground body has, when cut in a planenormal to the central axis of the honeycomb structure 1, a sectionalshape such as circle, oval, triangle, square or the like; and the groundbody is coated with a coating material 4 at the outer surface. When thehoneycomb structure 1 is used as a DPF and when it is provided in, forexample, an exhaust gas system of diesel engine, it can capture theparticulate (including soot) emitted from the diesel engine.Incidentally, in FIG. 1, cells 5 and partition walls 6 are indicatedonly in one honeycomb segment 2.

Each honeycomb segment 2 has such a shape that is part of the honeycombstructure 1 (see FIG. 1), as shown in FIGS. 3 and 4 and, when bonded toeach other in a direction normal to the central axis of the honeycombstructure 1 (see FIG. 1), forms the honeycomb structure 1. The cells 5are arranged so as to be parallel to each other in the central axisdirection of the honeycomb structure 1. At each end face of thehoneycomb segment 2, the ends of cells 5 adjacent to each other areplugged alternately by a plugging material 7.

In any given cell 5 (a gas-incoming cell), the end at the left side ofFIGS. 3 and 4 is open and the end at the right side is plugged by aplugging material 7. Meanwhile, in any other cell 5 (a gas-leaving cell)adjacent thereto, the end at the left side is plugged by the pluggingmaterial 7 but the end of the right side is open. By such plugging, eachend face of the honeycomb segment 2 comes to have a checked pattern suchas shown in FIG. 2.

When such a honeycomb structure 1 formed by bonding of a plurality ofhoneycomb segments 2 is provided in an exhaust gas system, an exhaustgas enters into the cells 5 of each honeycomb segment 2 from the leftside of FIG. 4 and moves to the right side.

FIG. 4 indicates a case wherein the left side of honeycomb segment 2 isan inlet of exhaust gas. An exhaust gas enters into the honeycombsegment 2 from the unplugged (open) side of each cell 5 (eachgas-incoming cell). The exhaust gas in the cell 5 (gas-incoming cell)passes through porous partition walls 6, enters into each other cell 5(each gas-leaving cell), and leaves the cell. During the passage of theexhaust gas through the partition walls 6, the particulate includingsoot, contained in the exhaust gas is captured by the partition walls 6.

In this way, the exhaust gas can be purified. By the above capturing,the particulate including soot deposits inside the honeycomb segments 2with the passage of time and the pressure loss of the honeycomb segments2 becomes larger. Hence, the honeycomb segments 2 are regenerated byburning the soot, etc.

In FIGS. 2 to 4 are shown honeycomb segments 2 having a square sectionalshape. However, the sectional shape may be a triangle, a hexagon or thelike. The sectional shape of cells 5 may also be a triangle, a hexagon,a circle, an oval or the like.

As shown in FIG. 2, a bonding material 9 is coated on the outer surfaceof each honeycomb segment 2 and functions so as to bond the honeycombsegments 2. Coating of the bonding material 9 may be conducted on therespective outer walls of honeycomb segments adjacent to each other but,between two honeycomb segments 2 adjacent to each other, may beconducted only on either one of two facing outer walls.

Such coating only on either one of two facing outer walls is preferredbecause the amount of the bonding material 9 used can be saved. Thethickness of the bonding material 9 applied is determined inconsideration of the bonding strength between honeycomb segments 2 andis appropriately selected in a range of, for example, 0.2 to 4.0 mm.

A coating material 4 is coated on the outer wall of the bonded bodyobtained by bonding of honeycomb segments 2 and functions so as toprotect the outer wall of the bonded body of honeycomb segments 2. Thethickness of the coating material 4 applied is appropriately selected ina range of, for example, 0.1 to 1.5 mm.

As the material for honeycomb segment 2, there is preferred, from thestandpoints of the strength and heat resistance, at least one memberselected from the group consisting of silicon carbide, silicon-siliconcarbide type composite material, silicon nitride, cordierite, mullite,alumina, spinel, silicon carbide-cordierite type composite material,silicon-silicon carbide composite material, lithium aluminum silicate,aluminum titanate and Fe—Cr—Al type metal. Of these, silicon carbide ora silicon-silicon carbide type composite material is referred.

The honeycomb segment 2 can be produced, for example, by adding, to amaterial appropriately selected from the above-mentioned materials, abinder (e.g. methyl cellulose, hydroxypropoxy cellulose, hydroxyethylcellulose, carboxymethyl cellulose or polyvinyl alcohol), a surfactant,water (as a solvent), etc., to prepare a body, extruding the body intothe above-mentioned shape, and drying the extrudate by a microwave, hotair or the like, followed by sintering.

As the plugging material 7 used for plugging of cells 5, the samematerial as for honeycomb segments 2 can be used. The plugging by theplugging material 7 can be conducted by masking those cells 5 not to beplugged and, in this state, immersing the end face of honeycomb segment2 in the plugging material 7 of slurry state to fill open (unmasked)cells 5. The plugging by the plugging material 7 may be conducted beforethe firing of formed honeycomb segment 2 or after the firing. However,the plugging before the firing is preferred because the firing step iscompleted only in one time of firing.

After the above production of honeycomb segment 2, each honeycombsegment 2 is coated, at the outer surface, with the bonding material 9of slurry state; a plurality of the resulting honeycomb segments 2 arebonded to each other so as to give an intended three-dimensional shape(the shape of honeycomb structure 1); in this bonded state,press-bonding is conducted; then, drying is made with heating; therebyis produced a bonded body wherein a plurality of honeycomb segments 2are bonded integrally. The bonded body is ground into theabove-mentioned shape; the ground body is coated with the coatingmaterial 4 at the outer surface, followed by drying with heating;thereby is produced a honeycomb structure 1 such as shown in FIG. 1.

The bonding material 9 contains a ceramic as a main component and aparticulate filler. The bonding material and the coating material may bethe same material. In the present embodiment, as the ceramic containedas a main component in the bonding material 9 and the coating material4, there can be mentioned, for example, ceramics such as siliconcarbide, silicon nitride, cordierite, alumina and mullite. Thereto maybe added a colloidal sol (e.g. colloidal silica or colloidal alumina)and, as necessary, a metal fiber and a pore former.

As the particulate filler contained in the bonding material 9 and thecoating material 4, there can be mentioned, for example, those composedof an inorganic material or an organic material. As specific examples ofthe inorganic material, there can be mentioned glass beads and fly ashballoons. As specific examples of the organic material, there can bementioned starch and a foamed resin.

The particulate filler has an average diameter of preferably 10 to 300μm, more preferably 15 to 250 μm, particularly preferably 20 to 200 μm.When the average diameter of the particulate filler is less than 10 μm,no filler effect of rollability is exhibited; the bonding material 9 andcoating material 4 are unable to show good coatability or spreadability;and suppression of drawbacks may be insufficient. Meanwhile, when theaverage diameter is more than 300 μm, the gaps between particles arelarge; as a result, the dehydration rate after coating is large, thesurfaces of the bonding material 9 and coating material 4 applied aredried quickly, no sufficient bonding strength is obtained in the case ofthe bonding material 9 even if honeycomb segments 2 to be bonded arepressed against each other, and drawbacks such as small holes, cracking,fretting and the like tend to generate in the case of the coatingmaterial 4.

The particulate filler is preferred to have a length ratio of majorcentral axis and minor central axis of 1.0 to 4.0 and is more preferredto be a true sphere.

The particulate filler is contained in the bonding material 9 or thecoating material 4 in an amount of preferably 20 to 70% by volume, morepreferably 25 to 65% by volume, particularly preferably 30 to 60% byvolume. When the amount is less than 20% by volume, no filler effect maybe obtained; when the amount is more than 70% by volume, no requiredstrength may be obtained.

The particulate filler is preferred to have a hollow structure. By usingparticles of hollow structure (hollow particles), the bonded areasformed by curing of the bonding material 9 and the outer surface formedby curing of the coating material 4 have lower densities, enabling areduction in Young's modulus. Thereby, the bonded areas and the outersurface have higher thermal shock resistances, and generation ofcracking during use can be suppressed.

In the present embodiment, the bonding material 9 and the coatingmaterial 4 may contain, in addition to the above-mentioned ceramic andparticulate filler, at least one member selected from the groupconsisting of inorganic particles, an oxide fiber and a colloidal oxidein an amount of 5 to 60% by mass. By containing them, the bondingmaterial 9 and the coating material 4 can have higher properties.

As the inorganic particles, there can be mentioned, for example, atleast one kind of ceramic selected from the group consisting of siliconcarbide, silicon nitride, cordierite, alumina, mullite, zirconia,zirconium phosphate, aluminum titanate and titania; a Fe—Cr—Al typemetal; a nickel type metal; metallic silicon; and SiC.

As the oxide fiber, there can be mentioned, for example, analuminosilicate-based fiber and other fibers.

As the colloidal oxide, there can be mentioned, for example, a silicasol and an alumina sol.

The bonding material 9 and the coating material 4 have a thermalconductivity of preferably 0.1 to 5.0 W/m·k, more preferably 0.2 to 3.0W/m·k. When the thermal conductivity is less than 0.1 W/m·k, the thermalconductivity between honeycomb segments 2 is hampered and thetemperature inside the honeycomb structure 1 may become non-uniform.When the thermal conductivity is more than 5.0 W/m·k, the bondingstrength may be reduced and it may become difficult to produce thehoneycomb structure 1.

The bonding material 9 and the coating material 4 are preferred to havea relatively low thermal expansion coefficient in order to prevent thegeneration of cracking caused by thermal shock, etc. The thermalexpansion coefficient is preferably 1×10⁻⁶ to 8×10⁻⁶/° C., morepreferably 1.5×10⁻⁶ to 7×10⁻⁶/° C., particularly preferably 2×10⁻⁶ to6×10⁻⁶/° C.

EXAMPLES

The present invention is described more specifically below by way ofExamples. However, the present invention is in no way restricted bythese Examples.

In the present Examples, a SiC powder and a Si powder both as a rawmaterial were mixed at a weight ratio of 80:20. To the resulting mixturewere added starch and a foamed resin (both as a pore former), methylcellulose and hydroxy propoxyl methyl cellulose, a surfactant and waterto prepare a plastic body. The body was extruded and the extrudate wasdried by a microwave and hot air to obtain a honeycomb segment having apartition wall thickness of 310 μm, a cell density of about 46.5cells/cm² (300 cells/in.²), a square sectional shape of 35 mm×35 mm, anda length of 152 mm.

The honeycomb segment was plugged at each end face by using the samematerial as used in production of the honeycomb segment, in such a waythat one cell was open at one end face and plugged at other end face,any cell adjacent thereto was plugged at the same one end face and openat the same other end face, and each end face showed a checked pattern.The honeycomb segment was then dried, degreased at about 400° C. in theair, and fired at about 1,450° C. in an Ar inert atmosphere to obtain afired honeycomb segment composed of Si-bonded SiC.

Meanwhile, there were mixed a foamed resin (an acrylonitrile resin) as afiller, methyl cellulose as an organic binder, a SiC powder as inorganicparticles, an aluminosilicate-based fiber as an oxide fiber, an aqueoussilica gel (40% by mass) solution and clay as an inorganic binder, andwater. Water was added thereto and the resulting mixture was kneaded for30 minutes using a mixer, to obtain bonded materials A to K whosecompositions are shown in Table 1. Of the bonded materials A to K shownin Table 1, the bonded materials A to I were used in the presentExamples and the bonded materials J and K were used in ComparativeExamples, as described later.

TABLE 1 Foamed resin Bonding Average Foamed Foamed Methyl SiCAluminosilicate material diameter resin resin cellulose powder fiberSilica gel Clay Water No. [μm] [mass %] [vol. %] [mass %] [mass %] [mass%] [mass %] [mass %] [mass %] A 15 1 40 0 41 24 23 1 10 B 100 1 40 0 4124 23 1 10 C 250 1 40 0 41 24 23 1 10 D 100 0.5 25 0 41 24.5 23 1 10 E100 4 65 0 40 24 22 1 9 F 5 1 40 0 41 24 23 1 10 G 500 1 40 0 41 24 23 110 H 100 0.2 10 0 42 25 22 0.8 10 I 100 7 80 0 40 23 22 1 7 J — 0 0 0 4225 22 1 10 K — 0 0 1 39 22 22 1 15

Table 2 shows the results obtained when viscosity measurement was madefor the bonding materials B, H and K shown in Table 1, during theirkneading at given time intervals. FIG. 5 shows the changes of viscositywith time when the bonding materials B, H and K were kneaded. In FIG. 5,the characteristic curve B1 shows when the bonding material B was used;the characteristic curve H1 shows when the bonding material H was used;and the characteristic curve K1 shows when the bonding material K wasused.

TABLE 2 Bonding Viscosity after Viscosity after Viscosity changeMaterial 5 minutes of 30 minutes of during kneading No. kneading [dPa ·s] kneading [dPa · s] [dPa · s] B 620 510 110 H 600 490 110 K 800 500300

As seen from these results, in the bonding material K (thecharacteristic curve K1) containing an organic binder, there is aviscosity increase at the initial period of kneading, but there issubstantially no viscosity change from around after 15 minutes. Incontrast, in the bonding material B (the characteristic curve B1) andthe bonding material H (the characteristic curve H1) both containing afoamed resin, there is substantially no viscosity change duringkneading.

Next, bonding of honeycomb segments was made using each of the bondingmaterials shown in Table 1. In each bonding, a plurality of thehoneycomb segments produced previously were bonded so that the thicknessof the bonding material used became 1 mm. The bonded honeycomb segmentswere dried at 200° C. for 5 hours to obtain honeycomb structures ofExamples 1 to 9 and Comparative Example 1. From each honeycombstructure, ten samples for strength test were cut out and measured forthree-point bending strength according to JIS R 1601. The results areshown in Table 3.

As shown in Table 3, in Comparative Example 1 using the filler-freebonding material (the bonding material J), large peeling was seen at thebonded area. In Examples 6 and 7 using the bonding materials F and Gwhich contained a foamed resin having an average particle diameterdeviating from the range of 10 to 300 μm, as well as in Examples 8 and 9using the bonding materials H and I which contained a foamed resin of anamount deviating from the range of 20 to 70% by volume, spreadability ofbonding material was insufficient and consequently peeling was seen onlyat part of the bonded area or the bonding strength was slightly small.

TABLE 3 Bonding Bonding material strength No. Appearance of bonded layer[Mpa] Example 1 A No peeling of bonded layer 2.9 Example 2 B No peelingof bonded layer 3.7 Example 3 C No peeling of bonded layer 2.7 Example 4D No peeling of bonded layer 3.3 Example 5 E No peeling of bonded layer3.2 Example 6 F Partial peeling of bonded 1.2 layer Example 7 G Nopeeling of bonded layer 0.9 Example 8 H Partial peeling of bonded 1.2layer Example 9 I No peeling of bonded layer 0.7 Comparative J There ispeeling. 1.4 Example 1

For Example 10 and Comparative Example 1 using the bonding materials Band J, respectively, comparison of density or strength/Young's modulusratio was compared. The results are shown in Table 4.

In Table 4, it was confirmed that strength/Young's modulus ratio waslarger in Example 10 using the bonding material B containing a hollowfoamed resin than in Comparative Example 1 using the bonding material Jcontaining no foamed resin. Thereby, improvement in thermal shockresistance during use can be expected.

TABLE 4 Bonding Young's Strength*1000/ material Density Strength modulusYoung's No. [g/cm³] [Mpa] [Gpa] modulus ratio Example 10 B 1.5 1.2 0.81.5 Comparative J 2.1 1.4 1.2 1.2 Example 1

Water was added to each of the bonding materials A to J for viscosityadjustment necessary for coating, whereby were produced coatingmaterials L to U. 16 fired honeycomb segments produced previously abovewere bonded to each other to obtain a bonded body. The outer wall of thebonded body was ground and then coated with one of the coating materialsL to U, followed by drying at 200° C. for 2 hours, to obtain honeycombstructures of Examples 11 to 19 and Comparative Example 3. In Table 5are shown the amount (mass %) of added water and the appearance ofcoating layer (small holes, cracking and friction) of each honeycombstructure which was examined visually.

TABLE 5 Added water Coating [mass % relative Appearance of coating layermaterial to bonding Small Crack- Fric- No. material] holes ing tionExample 11 L 2.0 No No No Example 12 M 2.0 No No No Example 13 N 2.0 NoNo No Example 14 O 3.0 No No No Example 15 P 2.0 No No No Example 16 Q2.0 No No Yes Example 17 R 2.0 No Yes No Example 18 S 3.5 No Yes NoExample 19 T 2.0 No Yes No Comparative U 4.0 Yes yes Yes Example 2

As indicated in Table 5, drawbacks of small holes, cracking and frictiongenerated in Comparative Example 2 using the filler-free coatingmaterial U. A sight drawback of cracking or friction generated inExamples 16 to 19 using the coating materials Q and R which contained afiller having an average particle diameter deviating from the range of10 to 300 μm, or the coating materials S and T which contained a fillerin an amount deviating from the range of 20 to 70% by volume.

INDUSTRIAL APPLICABILITY

The honeycomb structure of the present invention is useful as a filterfor exhaust gas, for example, as a diesel particulate filter (DPF) forcapturing and removing the particulate contained in an exhaust gasemitted from a diesel engine or the like.

1. A honeycomb structure comprising: a plurality of honeycomb segrnentseach of which has a plurality of cells surrounded and defined by porouspartition walls to form a honeycomb structure as a whole, and each ofthe cells functions as a passage of a fluid, and is arranged to beparallel to each other in a central axis direction of the honeycombstructure, wherein each segent is bonded integally at least at its twoouter partition walls to other adjacent segments by a bonding materialin a direction normal to the central axis direction to form thehoneycomb structure, the bonding material containing a ceramic as a maincomponent. and a foamed resin having an average particle diameter of 15to 250 μm and being contained in 25 to 65 volume percents with relationto total volume of the bonding material, the foamed resin promotingcoatability and spreadability of the bonding material by virtue ofrollability of the foamed resin, whereby the bonding material with thefoamed resin has less suppression in shrinkage caused by dehydration,and is substantially free from peeling and cracking.
 2. A honeycombstructure according to claim 1, wherein the bonding material furthercontains at least one member selected from the group consisting ofinorganic particles, an oxide fiber and a colloidal oxide.
 3. Ahoneycomb structure according to claim 1, wherein an amount of thefoamed resin used in the bonding material is 0.5 to 4 percents byweight.
 4. A honeycomb structure according to claim 1, wherein thebonding material has a bonding strength of 1.2 MPa or more.
 5. Ahoneycomb structure comprising: a plurality of honeycomb segments eachof which has a plurality of cells surrounded and defined by porouspartition walls to form a honeycomb structure as a whole; each of thecells functions as a passage of a fluid, and is arranged to be parallelto each other in a central axis direction of the honeycomb structure,each segment being bonded integrally at least at its two outer partitionwalls to other adjacent segments by a bonding material containing aceramic as a main component; an outer wall formed of a plurality ofsegments bonded with the bonding material, the outer wall being ground;and a surface coat layer formed on an outer surface of the outer wall,wherein the surface coat layer has a coating material containing aceramic as a main component, and a foamed resin having an averageparticle diameter of 15 to 250 μm and being contained in 25 to 65 volumepercents with relation to total volume of the coating material, thefoamed resin promoting coatability and spreadability of the coatingmaterial and coating material and promoting suitable viscosity of thecoating material for coating, whereby the surface coat layer issubstantially free from small holes, cracks and fractions in itssurface.
 6. A honeycomb structure according to claim 5, wherein thecoating material further contains at least one member selected from thegroup consisting of inorganic particles, an oxide fiber and a colloidaloxide.
 7. A honeycomb structure according to claim 5, wherein an amountof the foamed resin used in the coating material is 0.5 to 4 percents byweight.
 8. A honeycomb structure according to claim 5, wherein thecoating material has a bonding strength of 1.2 MPa or more.